In fact, "The Well Grounded Rubyist" is a "reworking" of "Ruby for Rails". The author mentions this relationship between the books in his "about this book" sect

In fact, "The Well Grounded Rubyist" is a "reworking" of "Ruby for Rails". The author mentions this relationship between the books in his "about this book" section at the beginning of "The Well Grounded Rubyist".